Add hb_buffer_clear()

Which is like _reset(), but does NOT clear unicode-funcs.

src/hb-buffer-private.hh

@@ -133,6 +133,7 @@ struct hb_buffer_t {
   /* Methods */
 
   HB_INTERNAL void reset (void);
+  HB_INTERNAL void clear (void);
 
   inline unsigned int backtrack_len (void) const
   { return have_output? out_len : idx; }

src/hb-buffer.cc

@@ -142,6 +142,15 @@ hb_buffer_t::reset (void)
   hb_unicode_funcs_destroy (unicode);
   unicode = hb_unicode_funcs_get_default ();
 
+  clear ();
+}
+
+void
+hb_buffer_t::clear (void)
+{
+  if (unlikely (hb_object_is_inert (this)))
+    return;
+
   hb_segment_properties_t default_props = _HB_BUFFER_PROPS_DEFAULT;
   props = default_props;
 
@@ -722,6 +731,12 @@ hb_buffer_reset (hb_buffer_t *buffer)
   buffer->reset ();
 }
 
+void
+hb_buffer_clear (hb_buffer_t *buffer)
+{
+  buffer->clear ();
+}
+
 hb_bool_t
 hb_buffer_pre_allocate (hb_buffer_t *buffer, unsigned int size)
 {

src/hb-buffer.h

@@ -135,6 +135,10 @@ hb_buffer_get_language (hb_buffer_t *buffer);
 void
 hb_buffer_reset (hb_buffer_t *buffer);
 
+/* Like reset, but does NOT clear unicode_funcs. */
+void
+hb_buffer_clear (hb_buffer_t *buffer);
+
 /* Returns false if allocation failed */
 hb_bool_t
 hb_buffer_pre_allocate (hb_buffer_t  *buffer,

test/api/test-buffer.c

@@ -128,7 +128,27 @@ test_buffer_properties (fixture_t *fixture, gconstpointer user_data)
   g_assert (hb_buffer_get_language (b) == hb_language_from_string ("Fa", -1));
 
 
-  /* test reset clears properties */
+
+  /* test clear clears all properties but unicode_funcs */
+
+  hb_buffer_clear (b);
+
+  g_assert (hb_buffer_get_unicode_funcs (b) == ufuncs);
+  g_assert (hb_buffer_get_direction (b) == HB_DIRECTION_INVALID);
+  g_assert (hb_buffer_get_script (b) == HB_SCRIPT_INVALID);
+  g_assert (hb_buffer_get_language (b) == NULL);
+
+
+  /* test reset clears all properties */
+
+  hb_buffer_set_direction (b, HB_DIRECTION_RTL);
+  g_assert (hb_buffer_get_direction (b) == HB_DIRECTION_RTL);
+
+  hb_buffer_set_script (b, HB_SCRIPT_ARABIC);
+  g_assert (hb_buffer_get_script (b) == HB_SCRIPT_ARABIC);
+
+  hb_buffer_set_language (b, hb_language_from_string ("fa", -1));
+  g_assert (hb_buffer_get_language (b) == hb_language_from_string ("Fa", -1));
 
   hb_buffer_reset (b);